Anode for magnesium primary cell



Sept. 13, 1960 R. c. KIRK ETAL ANODE FOR MAGNESIUM PRIMARY CELL .9 .917 dispel-sea;

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INVENTORS. Roy 6. Kirk John L Robinson N m r r A United States Patent AN ODE FOR MAGNESIUM PRIlVIARY CELL Roy C. Kirk and John L. Robinson, Midland, Mich., as-

signors to The Dow Chemical Company, Midland, Mieh., a corporation of Delaware Filed Apr. 4, 1957, Ser. No. 650,750

4 Claims. (Cl. 136-120) This invention relates to an improved anode for use in a primary magnesium battery cell whereby the normal delayed action usually resulting from the employment of such a battery cell is decreased.

It has been well established that primary cells utilizing magnesium as the anode, carbon depolarized with manganese oxide as the cathode and a bromide of an alkali metal, alkaline earth metal or ammonium as an electrolyte have specific advantages in certain uses. For example, a greater capacity per unit of volume is generally achieved. One of their disadvantages, however, is that r the cells do not always attain full working voltage immediately on attempting to reuse them following a rest period. This delayed action may vary from 0 to as much as 100 seconds or more depending upon the specific composition of the components of the cell, the amount of use that has been made of the cell, the intervening rest period, and the age of cell.

It is a principal object of the present invention to provide an anode material for a magnesium primary cell which results in a shorter delayed action when employed in the conventional magnesium primary cell. Still another object of the present invention is to provide an improved magnesium anode material containing substantial quantities of massive Mg Al compound. A further object of the present invention is to provide an improved anode material for magnesium primary cells which is prepared by the rapid cooling of a magnesium aluminum alloy from a temperature above its solidus and below its liquidus temperatures. Another object of the present invention is to provide a magnesium anode material for primary cells containing from 0.5 to 12 percent aluminum, a substantial proportion of which is present as massive Mg17A112 compound. Other objects will become apparent hereinafter.

The foregoing and additional objects have been accomplished by providing a magnesium cell having a mag nesium anode in which a part of the magnesium is present as massive Mg Al compound.

Magnesium batteries have been described in a number of US. patents including US. Patents 2,547,907, 2,616,- 940, 2,712,564, etc. These patents all rely upon a magnesium anode, a cathode into which has been mixed a depolarizing agent such as manganese dioxide and an alkaline metal, alkaline earth metal, or ammonium bromide electrolyte, an anode liner, and a carbon current collector. The present invention specifically relates to an improvement in the anode of such a cell whereby the delayed action is substantially reduced. Provision of such anode is accomplished by heating a magnesium alloy containing from 1 to 12 percent aluminum to a temperacure above its solidus temperature but below its liquidus temperature and rapidly cooling this m aterial so that a massive Mg17Al12 compound is formed. Representative alloy materials which are suitable are those magnesium base alloys containing at least 80 percent, preferably 90- percent magnesium and containing from 1 to 12 percent lCe aluminum, preferably from 1 to 9 percent aluminum, from 0.0 to 3.0 percent zinc, from 0.0 to 0.5 percent calcium, the balance being commercial magnesium containing not over 0.005 percent iron, not over 0.002 percent nickel, and not over 0.6 percent manganese. This alloy is heated to a temperature above its solidus temperature, and below its liquidus temperature, both of which will vary depending upon the particular alloy being employed. After heating to this temperature, the alloy material is rapidly cooled as by quenching, etc., that is, at a rate of at least 500 Fahrenheit degrees per mintute, preferably about 1000 Fahrenheit degrees per mintue, and when so cooled, results in substantial quantities of massive Mg17A112 compound being formed therein. The rapid cooling should be carried to a point below that which the massive Mg17Al12 compound will be stabilized and not converted to fine Mg Al compound or another MgAl composition. This temperature is below the eutectic temperature, usually below 700 degrees Fahrenheit and preferably below 500 degrees Fahrenheit. Slower cooling techniques may result in fine particles of Mg Al compound being formed. It has been established that these fine particles adversely affect the magnesium alloy when used as an anode in magnesium primary cells by increasing the delay time. Therefore, it is essential that the anodes of the present invention contain massive Mg Al particles. Alternatively, the magnesium alloy may be heated to above its liquidus temperature and thereafter rapidly cooled, as in a die-cast technique. This constitutes a preferred embodiment for forming the anodes of the present invention. While die-casting is the preferred technique for forming the anodes of the present invention,

quenching of the alloy after heating above its solidus taining massive Mg Al present may be machined or otherwise formed to obtain the desired final shape for the anode, provided however, that such forming operations are not suificiently drastic to eliminate the presence of the massive Mg17A112 compound.

The anodes so prepared are used in a conventional manner in a magnesium primary cell. The advantages of employing such an alloy are many, but primarily are represented in the decreased delayed action of a cell employing such an anode.

The following examples are given to illustrate the anodes of the present invention but are not to be con-- strued as limiting the invention thereto;

EXAMPLE I Two alloy compositions, one of which contains 3 per cent aluminum and 1 percent zinc, the remainder being commercial magnesium (AZlOA) and the second of which contains 1 percent aluminum and 0.4 percent zinc, the remainder being commercial magnesium (AZIOA) were both extruded and die-cast to form anodes for primary magnesium cells.

chromate were employed. Different cells containing the extruded and die-cast anodes were tested in three standard tests: the Railroad Lantern'test utilizing an alternate discharge time and rest time of 30 minutes during an 8-hour day with a subsequent rest time of 16 hours, 7 days per week, on a 32 ohm load for a, 3-cell pack; the

Cells containing these alloys as anodes, a cathode of 91 percent manganese dioxide, 3 percent barium chromate and 6 percent acetylene black,:. and an electrolyte containing 250 grams per'liter of magnesium bromide and 0.36 gram per liter of sodium the improved delay properties.

general purpose test of 5' minutes discharge through 4- ohms per cell per day, 7 days per week and the BA-30 test of 4 minutes discharge through 6.75 ohms per cell out of 30 minutes for 10 hours per day, 5 days a week; The following table summarizes the results obtained from these-tests;

cient to provide the improved anode of the present invention, alloy AZ31A was heated at various temperatures for 1 hour and quenched in water to provide a rapid cooling. The following table shows that heating 5 above the solidus temperature is essential to provide the massive Mg17A112 required by the present invention.

N0'1E.-IJ1 the above table, the AM delay is measured during the first discharge of that days test, the PM delay is measured during the final discharge of that days test.

Table I illustrates that massive Mg17A112 compound is required to achieve the reduced delay time of the present invention. Die-cast forming causes massive- Mg Al compound to be present while extrusion does not cause its presence.

EXAMPLE II The procedure of Example I. was repeated with alloy AZ31A (3 percent aluminum, 1 percent zinc, remainder magnesium) and AZ9'1A (9 percent aluminum, 1 percent zinc, remainder magnesium) and a variety of fabrication methods used to form the anode. The following table summarizes the results obtained.

Table III 25 General Purpose Test Delay, Seconds Heat-Treat Temperature 7 Max. Ave.

3 1.8 3 1. 6 3' l. 5 3 1'. 8 a 1. s 3 2.0 3 1. 5 2. 8 1. 2 1. 2 0.1

1 Above the Solidus Temperature.

Table II TESTS Railroad Lantern Delay, Seconds GeneralPurpose Anode T Delay, Seconds Compo- Slug. 'ype sition AM' PM Max. Ave. M'ax. Ave. Max Ave.

AZ31A--. Impact extruded-Ex- I s 4.6 15 10.6 5 2.9

truded' slugs. AZ3lA Impact extruded-Die- 2.3 1.8 8 4.7 3.2 15

cast slugs. AZ31A.-- Die-cast 2.0 1.2 5 2.4 0 AZSIA--- Die-cast heat treat-800 5.5- 4.6. 10 7.2 3 2.1

F-lfi' Hrs.Furna;ee coo AZBIA.-- Die-cast heat treat1120 2.0 1.2 2.5 0

F. 2 hI'S.-H3O quench. V AZQIA--- Die-cast..- 13 8.5 V 7 5.3 2' 1.4 .AZQlA--- Die-cast h treat-800 49 25.0 12 2.9 3 1.9 152-116 hrs.-Furnace coo 1 Abovethe Solidus Temperature.

-sive MglqAlm compound; while the second. method does 'not form this material.

Alternatively, impact extrusion ofa die-cast slug retains suflicient massive 'Mg Al compound to cause improved delay action. The tabl'e also illustrates that massive Mg17A112 compound can be destroyed by solution heat treatment, with the loss" of EXAMPLE To illustrate that heat treatment by itself is 'not'sufi- 75 70 nesium alloy containing from 1 to 12 percent aluminum 2. A process for preparing an anode for use in a primary magnesium cell which comprises heating a magnesium alloy containing from 1 to 9 percent aluminum to a temperature of about 1130 degrees Fahrenheit, cooling the resulting heated alloy at a rate greater than 1000 Fahrenheit degrees per minute.

3. A primary battery cell comprising an anode of magnesium having massive Mg Al compound dispersed therein, a manganese dioxide depolarized cathode, and an electrolyte comprising an aqueous solution of an inorganic bromide selected from the group consisting of the alkali metal, alkaline earth metal and ammonium bromides.

4. An anode for a primary magnesium cell which comprises an alloy which has been formed by die casting, said alloy containing from 1 to 12 percent aluminum, fiom 0.0 to 3.0 percent zinc, from 0.0 to 0.5 percent calcium, the balance being commercial magnesium containing not over 0.005 percent iron, not over 0.002 percent nickel, and not over 0.6 percent manganese.

References Cited in the file of this patent UNITED STATES PATENTS 1,850,612 Wood et a1 Mar. 22, 1932 2,616,940 Reid Nov. 4, 1952 2,621,220 Kirk et a1. Dec. 9, 1952 OTHER REFERENCES UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2,952,727 September 13, 1960 M Roy C. Kirk et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 58, for '"AZ1OA" read AZ3lA Signed and sealed this 16th day of May 1961.

(SEAL) Lttest:

ERNEST W. SWIDER DAVID L. LADD Lttesting Officer 7 Commissioner of Patents 

4. AN ANODE FOR A PRIMARY MAGNESIUM CELL WHICH COMPRISES AN ALLOY WHICH HAS BEEN FORMED BY DIE CASTING, SAID ALLOY CONTAINING FROM 1 TO 12 PERCENT ALUMINUM, FROM 0.0 TO 3.0 PERCENT ZINC, FROM 0.0 TO 0.5 PERCENT CALCIU, THE BALANCE BEING COMMERCIAL MAGNESIUM CONTAINING NOT OVER 0.005 PERCENT IRON, NOT OVER 0.002 PERCENT NICKEL, AND OVER 0.6 PERCENT MANGANESE. 